(a) Field of the Invention
The present invention is related to a method to drive a display of grid array pixels, and more particularly to one that has grayscale code range of each light color mapped to an adjusted range and to overdrive pixels to present the luminance desired for the response time of the pixel to be shorter than the frame time, thus to solve the problem of residual image.
(b) Description of the Prior Art
Reason for LCD to get popular is that in comparison with the conventional CRT display, LCD provides advantage of low power consumption, compact, radiation free and absence of glittering to make it applicable to TV, notebook or PC screen and gradually becomes the mainstream in the manufacturing industry of display. Furthermore, with the advancing process technology of display and the introduction of large size LCD, LCDs become even more comprehensively applied in daily life and A/V entertainment. Meanwhile, more demands are particularly put on the visual angle, response speed and number of colors of the display to pursue even higher quality presentation of image of the display.
Conventional CRT display works on having electronic beams to irradiate from the terminal of a vacuum tube to a screen coated with light emitting material; the irradiated screen produces momentary colors, meaning they will disappear before the irradiation of the image data of the next picture. That type of display refers to impulse type, and there will be no residual image between pictures; however, glittering does exist if the scanning frequency of the CRT display is not fast enough.
On the contrary, there will be no problem of glittering in case of a LCD because LCD contains a liquid crystal capacitor CLC and storage capacity (CS) so that the voltage to drive liquid crystal molecules is stored in a fully charged capacitor to be held for the next updated picture. This type of display is referred to as a hold type. However, if the response rate of liquid crystal molecules when driven by the voltage is not fast enough, i.e., the response time is greater than the frame time, the picture will become blur or produce residual image to significantly affect the viewing quality.
As illustrated in FIGS. 1, 2A, and 2B, generally the response time is divided into two parts: (1) Rising response time (Tr): i.e., with the applied voltage, the time raising taken for the luminance of the liquid crystal box of the LCD to change from the level of 10% up to 90%; and (2) Falling response time (Tf), i.e., without the applied voltage, the time falling taken for the luminance of the liquid crystal box to change from the level of 90% down to 10%. If the curve of the variation of the normal luminance is indicated as “10” for a display to receive the image of code A during the first frame time I and the image of code B during the second frame time II, the expected luminance of code B may be achieved only upon entering into the firth frame time III in case of a display with the response rate of its liquid crystal molecules. Furthermore, if the display relates to a hold type, problems of deferred or residual image will appear as illustrated in FIG. 2B, wherein, the arrow points out the scanning direction of the display. If overdrive method is used to have the second frame time II of the display to drive with and OD voltage higher than that of code B and the response rate of the liquid crystal molecules is fast enough, the luminance variation may reach the expected luminance with that frame time with its luminance curve as that marked by 10′. Even so, certain residual image problem remains in case of a hold type display with its scanning picture as illustrated in FIG. 2B.
To solve the problem of residual image, the impulse type of CRT display is usually borrowed in the following two approaches: (1) Data of black color or black pictures are inserted into pictures of continuous images; and (2) Signals of black picture are inserted into back light source to control the light source for producing flaring effects so to glitter the back light source. As illustrated in FIGS. 3A when the first approach is applied to insert black pictures into picture of image, the grayscale code of the image of the first frame time I is code A, data of black picture are received upon entering into the first black picture time I′ for the luminance variation curve 20 to indicate as an impulse curve. Upon entering into the second frame time II, the third frame time III and the fourth frame time IV, code B with a luminance higher than that of code A is received while data of black pictures will immediately following after each grayscale code B, e.g., the second black picture time II′, the third black picture time III′ and the fourth black picture time IV′. Theoretically, any pixel driven by code B shall give the same luminance performance, i.e., the highest points of the luminance curve shall be at the same level. However, lab test shows that the luminance is gradually rising with the luminance of any frame time higher than that of the immediately preceding one, a phenomenon so far not yet explained by any theory in the field of liquid crystal. As projected, the sticking characteristic of liquid crystal molecules might be attributable to such phenomenon. Nonetheless, the problem should be solved to avoid poor picture quality or insufficient luminance of the picture to indicate the delay as illustrated in FIG. 3B.